1. Field of the Invention
The present invention relates to a tapered fiber that can constitute napped fabrics having good hand with anti-drape stiffness, termed "HARI" in Japan, and stiffness, termed "KOSHI" in Japan, and excellent color developing property and depth of color and causing, after being sewn, no white appearance along seams. More specifically, the present invention relates to polyester fiber-based napped fabrics usable in a wide variety of uses such as interior fabrics, e.g. car seats and carpets, artificial suedes and clothing and to tapered fibers constituting the nap of such fabrics.
2. Description of the Prior Art
Napped fabrics such as standard cut-pile, moquette, double-raschel, velour and velvet have various appearances and hands and have been widely used as interior fabrics including car interior fabrics such as car seat covers, household interior fabrics such as carpets and flocked fabrics, artificial suedes and wearing apparel.
Fibers comprising polyester, in particular polyethylene terephthalate, are widely used for clothing, industrial purposes and interior fabrics.
In recent years in particular, polyethylene terephthalate fibers are penetrating rapidly into the field of car interior napped fabrics, utilizing its excellent light-fastness. However, napped fabrics comprising polyethylene terephthalate fiber have stiffer tactility and are significantly poorer in appearance such as luster and brightness, than those made of fibers of acrylic, nylon, rayon, silk, wool and the like. Besides, when these polyester fiber-based napped fabrics are dyed, they hardly give mild luster like that of napped fabrics comprising natural fibers such as wool and silk because of the surface of the fibers being smooth, and their hand lacks natural feeling, and it is difficult to give them deep color.
To make deep the color of dyed napped fabrics, it is generally recommended to use a super bright type of polyester fiber, containing no inorganic fine particles. However, although napped fabrics using this type of fiber for their nap have improved color development, they give a shining appearance depending on the angle seen and lack high-quality feeling. To eliminate this shining appearance, polyester fibers of semi-dull type containing a small amount of titanium oxide are being used for naps, which, however, deteriorates color developing property of the napped fabrics and make them look whitened when dyed in light colors. Such napped fabrics cannot produce high-quality feeling.
Furthermore, polyester fiber-based napped fabrics give, when dyed, different color shades depending on the angle seen, thereby creating variation in luster and depth of color. As a result they often show partly blackish and partly whitened as if covered with dust. Such napped fabrics further have a drawback that, when sewn, their raised fibers fall down along the seam and look whitish, i.e. what is known as "whitened seam", which impairs the high-quality feeling to a large extent. This is attributable to the fabrics having large surface reflection caused by large refractivity and smooth surface of the polyester fibers used and also to reduced color developing property due to large difference between the reflectivities of the side surface and cross-section of the polyester fibers.
Various proposals have been made to solve the above problems, i.e. to improve the color developing property of polyester fiber to be used for raised fibers of napped fabrics.
For examples, Japanese Patent Application Laid-open No. 268855/1987 discloses a sheath-core composite fiber comprising a core of polyester and a sheath of a cationically dyeable polyester. In this fiber, the sheath is dyed in a deeper color compared with the core, so that the side surface of the fibers become not so distinguishable even when exposed on the surface of the napped fabric containing them. However, the sheath, having been dyed with a cation dye to produce deep color, has poor lightfastness and hence napped fabrics utilizing such fibers are often unusable depending on the use.
Japanese Patent Application Laid-open No. 124858/1991 disclose a pile fabric comprising sheath-core composite polyester fibers with their core containing a larger amount of titanium oxide compared with their sheath so that the mirror reflection of the fiber side surface is reduced and does not differ so much from that of the fiber cross-section. Japanese Patent Application Laid-open No. 306646/1989 discloses a pile fabric comprising sheath-core composite fibers and having good color development and, at the same time, no shining appearance by adding an inorganic fine powder having high refractivity to the sheath only. However, incorporation of an inorganic fine powder having high refractivity such as titanium oxide to the core and/or sheath of a sheath-core composite fiber permits the surface reflectivity the fiber cross-section to become close to that of the fiber side surface, thereby being unable to solving the problems of white appearance, whitened seams and the like due to severe falling down of raised fibers, of the napped fabrics comprising such fibers as their naps.
It is known that roughening of the side surface of polyester fibers reduces the surface reflectivity because light incident on the roughened surface repeats zigzag reflections in the recesses and is eventually absorbed into the fibers. Japanese Patent Application Laid-open No. 214412/1992 discloses a napped fabric, utilizing the above technique, comprising raised fibers of sheath-core composite polyester fibers having roughened side surface to decrease the reflectivity of the fiber surface and being tapered to the ends to cause irregular reflection of light there, thereby increasing the surface reflectivity. With such polyester fibers, the difference between the surface reflectivities of the fiber cross-section and the fiber side surface becomes small and hence napped fabrics having a nap of such fibers no longer suffer from dark fading or white appearance. However, the problem of uneven color occurring with extreme falling down of raised fibers, such as whitened seams, cannot be solved completely with the napped fabrics with a nap comprising such fibers.